GB2031600A

GB2031600A - Heat-sensitive recording paper

Info

Publication number: GB2031600A
Application number: GB7923992A
Authority: GB
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 1978-07-18
Filing date: 1979-07-10
Publication date: 1980-04-23
Also published as: JPS6043318B2; JPS5514281A; US4255491A; GB2031600B; DE2929102C2; DE2929102A1

Description

1

SPECIFICATION

Heat-sensitive recording paper GB 2 031600 A 1 This invention relates to heat-sensitive recording paper capable of forming a dye image which lasts well 5 under high temperature and high humidity conditions.

In heat-sensitive recording papers images are formed utilizing physical or chemical changes induced in the recording materials by heat energy, and a large number of processes using heat-sensitive recording papers have been investigated.

_10 One type of heat-sensitive recording paper which relies upon a heatinduced physical change is wax-type 10 heat-sensitive recording paper which is well known and has been used for recording electrocardiograms and the like. Other types of heat-sensitive recording paper utilize a heatinduced chemical change to form images and a number of materials relaying on various different color-forming mechanisms have been proposed; of these, a binary coloration system is most common.

A material relying on a binary coloration system is prepared by dispersing two heatreaCtiVeCOMOOUnds 15 in fine particulate form in a binder or the I ike such that the binder separates them from each other, and coating the resultant mixture on a base paper. The thus-prepared paper- records images on heating it to melt one or both of the compounds such that they come into contact with each other, thus causing a color-forming reaction. These two heat-reactive compounds are generally referred to as electron-donating compounds and electron accepting compounds, respectively. An extremely large number of combinations 20 of them are known, and they are roughly classified as systems forming images of a metal compound and systems forming dye images.

Representative examples of systems forming images of a metal compound are those in which the electron-donating compounds are organic reducing agents such as phenols, chelating agents, sulfur compounds, or amino compounds, and the electron-accepting compounds are organic metal salts. These two produce a metal, metal complex compound, metal sulfide or the like through the reaction therebetween upon being heated, thus providing a colored image. Specifically, there are a combination of thiourea and heavy metal salt (U.S. Patent 2,740,895), a combination of gallic acid or the like and metal salt of stearic acid (U.S. Patents 2,663,654, 2,663,655, 2,663,656, and 2,663,657), a combination of hydroquinone and silver behenate (U.S. Patent 3,031,329), and a combination of hexamethylenetetramine and tin compound (U.S.

Patent 2,813,043.

On the other hand, examples of systems forming dye images are those in which the electron-donating compound is an electron-donating colorless dye, and the electron- accepting compound is an acidic material such as phenol orthe like (Japanese Patent Publication No. 4,160/68 and U. S. Patent& 3,451,338; 3,539,375; 3,674,535 and 3,666,525).

25' These binary coloration systems of heat-sensitive recording papers have many advantages as recording papers. For example: (1) they are based on primary coloration and do not require development processing; (2) the paper quality is similar to that of ordinary paper; and (3) they are handled with ease. In particular, those materials wherein a colorless dye is used as the electron-donating compound have the additional advantages that (4) they provide higher color density and (5) they enable one to easily obtain heat-sensitive 40 recording papers forming different colors, and are thus more valuable. Therefore, they are in most use as heat-sensitive recording papers.

Above all, those papers in which a bisphenol derivative represented by the following general formula:

R 1 45 -ON RZ wherein R, and R2 each represents an alkyl group containing 1 to 12 carbon atoms (e.g., R, may be a methyl 50 group or an ethyl group while R2 is a methyl, an ethyl, a propyl, an n- buty], an n-octyi, an n-decyl, an iso-butyl, or an iso-heptyl group) or, when taken together, R, and R2 form a saturated carbocyclic ring (i.e., cyclohexyl), is used as an electron-accepting compound exhibit high coloration sensitivity and provide high coloration density. However, they have several defects. One defect is that they form increased background fog when stored under high temperature and high humidity conditions. Conventional binary coloration systems in heat-sensitive recording papers form an increased background fog during storage under high humidity even when the temperature is lower than the temperature atwhich the coloration reaction takes place. This is not favorable in the paint of storage stability. Thistendency is particularly serious when paper is used as a support as compared with the case when a plastics film or metal is used as a support.

It is therefore an object of the present invention to provide a heatsensitive recording paper showing 60 excellent storage stability under conditions of high temperature and high humidity.

As a result of investigating various means to attain this object, it has been discovered that a heat-sensitive recording paper exhibiting exceptionally good storage stability under conditions of high temperature and high humidity can be obtained by controlling the hot waterextraction pH of the base paper is about 6 to 9.

The term "hotwater extraction pH" as used herein means the pH of the extractobtained by extracting a 65 2 GB 2 031 600 A 2 sample piece of base paperwith hotwater as specified in JIS-P-8133-1976, (hereinafter abbreviated as extraction pH). 20 me of the distilled water is added to about 1.0 g of sample pieces in a 100 m'Erienmeyer flask. The sample pieces are uniformly immersed in the distilled water using a stirring rod. 50 ml'of distilled water is added to the obtained mixture and the mixture is stirred. The mixture is then placed in a flask equipped with a condenser and heated on a water bath maintained at 95 to 1 00'C for one hour while 5 occasionally shaking the flask without boiling the water. The solution is cooled to a temperature of 20'C 5 deg. The pH of the extract obtained at a temperature of 20'C 5' is the extraction pH.

Several recording papers prepared by providing a recording layer on a base paper with an extraction pH of around neutrality have been proposed (for example, Japanese Patent Publication No. 6,645177). However, such recording papers have only been used for pressure sensitive recording papers and the electron accepting compounds used are different from those used in the present invention. Such papers have not been used in heat sensitive recording papers. In the case of the heat sensitive recording papers, the electron-accepting compound and the electron-donating colorless dye exist in the same layer, and under the condition of high temperature and high humidity they react with each other to cause coloration.

In the heat sensitive recording paper of the present invention the coating property of a coating solution is 15 improved and the contamination of the hot pen and hot head used for recording with color forming components is prevented. When smoothness and water resistance are required, a wax such as paraffin wax, polyethylene wax or higher fatty acid (ethyl enebistea ram ide, stearic acid amide) are added.

Generally, coating is carried out in a conventional manner (e.g., by air knife coating, blade coating, roller coating, bar coating). The amount of coating solution is 2 to 10 g/M2. The drying is carried out such that the 20 temperature of the surface of the paper coated is lower than the temperature at which the coloration reaction takes place.

In orderto depress the coloration reaction, attempts have been made (1) to keep the pH of the coating composition alkaline, or (2) to incorporate an alkaline material such as magnesium oxide in the color-forming layer. However, such attempts have not been successful and it has been found that a heat-sensitive recording paper exhibiting less fog when stored under high temperature and high humidity conditions is obtained using a base paper with an extraction pH in the range of from neutrality to weak alkalinity as a support.

This effect is particularly great when a composition capable of forming color at comparatively low temperatures (70 - 1 OOOC) is used as the heat-sensitive color-forming layer.

As a process for producing a base paper used in the present invention, any sizing process that eventually provides an extraction pH of from neutrality to weak alkalinity can be employed. For this purpose, there are three types of sizing processes which are particularly suitable: (1) a process using a sizing agent which fixes itself onto the pulp fibers to exhibit its sizing effect; (2) a process using a non-acidic fixing agent or a sizing agent which provides an extraction pH around neutrality when used in combination with a fixing agent; and 35 (3) a process of surface-treating with a sizing agent. These processes (1), (2), and (3) may be combined with each other.

As the typical sizing agents for use in process (1), there are cationic sizing agents including (1) sizing agents emulsified with a cationic surface active agent, e.g., quaternary amines, and (11) inorganic or organic salts of alkylamines such as (1) a higher fatty acid amine hydrochloride (the term "higher fatty acid" as used herein 40 and below refers to a fatty acid having 8 or more carbon atoms such as stearic acid); (2) a higher fatty acid-alkanolamine condensate hydrochloride; (3) a higher fatty acid- polyalkylenepolyamine condensate hydrochloride; (4) a higher fatty acid amide hydrochloride; (5) a hydrochloride salt of the reaction product of a higher aliphatic amine and epichlorohydrin; (6) a fatty acid-acylated alkylenepolyamine/epichlorohydrin condensate; (7) a reaction product prepared by condensing ethylene oxide with a primary alkylamine, and 45 further reacting the product with epichlorohydrin; (8) a product prepared using rosin, maleoylated rosin, maleoylated xylene resin, maleoylated petroleum resin, ester gum, or the like in place of higher fatty acid in (1) - (6) above; (111) salts of homopolymers or copolymers of nitrogen- containing vinyl monomers such as (1) methyl styren e-vi nyl pyridi ne copolymer; (2) polyeyclohexylaminoalkyl acrylate; (3) N-vinylimidazol/alkyl acrylate copolymer; (M reaction products of a chlorinated compound and an amine such as (1) a quaternary 50 salt of vinylidene chloride/vinyl chloroacetate copolymer; (2) a reaction product of 1-chloromethy]-2,4 dimethylbenzene condensate and a trialkylamine; (3) a product prepared by chlorinating or chloromethylat ing methylstyrene, and converting to cation using pyridine.

There are also cationic sizing agents which are prepared by reacting a 1:1 condensate of methyl acrylate and polyethylenepolyamine with epichlorohydrin. These are described, for example, in U.S. Patent 2,772,967, Japanese Patent Publication No. 6,204/53, U.S. Patents 2,698. 793, 2,479,480 2,724,694, 2,964,445, 3,084,093, Belg. Pat. 625,363, Canadian Pat. 657,152, Japanese Patent Publication No. 13,682/65, 13.P. 864,336.

Process (2) uses a sizing agent in combination with a cationic fixing agent. Suitable sizing agents are anionic sizing agents such as ordinary rosin sizing agent, petroleum sizing agent, and reactive sizing agents such as alkylketene dimer, alkylsuccinic acid anhydride. Cationic fixing agents to be used in combination 60 with them are cationic high molecular electrolytes. Examples thereof include cation-converted starch, cation-converted urea-HCHO resin, dicyandiamine-HCHO resin, dicyandiamidemodified urea resin, cation converted polyacrylamide, polyethyleneimine, epoxy-modified polyamide resin. In addition, there are polyacrylic acid hydrazide prepared by converting sodium polyacrylate to hydrazide and cation-converted aliphatic acid amide.

or If V 0.1 r:

3 GB 2 031 600 A 3 Of the above-described sizing agents, reactive sizing agents such as alkylketene dimers and alkylsuccinic acid anhydrides, or fatty acid soaps containing 12 or more carbon atoms are effective in that they raise color density.

In process (3) any sizing agent for processes (1) and (2) can be used and process (3) is particularly preferred because no particular fixing agents are necessary.

The amounts of the sizing agent and the fixing agent added are properly selected based on the weight and thickness of the support, and the conditions for coating a color developer. Usually, the sizing agent is added in an amount of about 0.1 - 1.5 wt % as solids based on pulp, and the fixing agent in an amount of about 0.2 - 2.0 wt % as solids. However, the extraction pH of the support must be strictly controlled within the aforesaid range.

The electron-donating colorless dyes, or color-forming agents generally used in the present invention are so-called leuco dyes, many of which are used as colorless dyes for use in pressure-sensitive recording paper.

They react with an electron-accepting compound, or color developer, to form color.

To be specific, there can be illustrated triary1methane compounds, diphenylmethane compounds, xanthene compounds, thiazine compounds, spiropyran compounds. Several examples thereof are illustrated below. As the triarylmethane compounds, there are 3,3-bis(p- dimethylaminophenyl)-6dimethylaminophthalide (or Crystal Violet lactone), 3,3-bis(p-di m ethyl am in op henyl) phtha I ide, 3-(p dimethylaminophenyl)-3-(1,2-dimethylindol-3-yl)phthalide, 3-(pdimethylaminophenyl)-3-(2-methylindol-3- yl)phthalide.

As the diphenylmethane compounds, there are 4,4'-bisdimethylaminobenzhydrin benzyl ether, N- 20 halophenyl-leucoAura mine, N-2,4,5-trichloropheriylleuco Auramine. As the xanthene compounds, there are hodamine-B-anilinolactam, Rhodamine-B-(p-nitroanilino)lactam, Rhoda mine- B-(p-ch loroani I ino)[actam, 3 diethylamino-7-(dibenzylamino)-fluoran, 3-diethylamino-7phenylaminofluoran, 3-diethylamino-6-methyl-7 anilinofluoran, 3-diethylamino-7-(o-chloroanilino)-fluoran, 3diethylamino-7-(3,4-dichloroanilino)fluoran, 3 piperidino-6-methyl-7-anilinofluoran, 3-diethylamino-7-phenylfluoran. As the thiazine compounds, there are 25 benzoyl leucoMethylene Blue, p-nitrobenzyl leucoMethylene Blue. As the spiro compounds, there are 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran, 3,3'dichloro-spiro-dinaphthopyran, 3 benzyl-spiro-dinaphthopyran, 3-methyl-naphtho-(3-methoxybenzo)-spiropyran, 3-propyl-spiro dibenzopyran. These are used alone or in combination.

As the electron-accepting compound, or the color developer, there are used phenolic compounds, organic 30 acids or the metal salts thereof, hydroxybenzoic acid esters. In particular, phenolic compounds represented by the above formula and organic acids (e.g. aromatic carboxylic acids such as salicylic acid and its derivatives, for example, 3,5-di-tert-butylsalicyclic acid, 3,5-di-(a-m ethyl benzyl)-sa licycl i c acid and 3 octylsalicyclic acid) or the metal salts (e.g., Ae, Zn, Mg and Ca salts) thereof are desirable since they show a high color-developing ability and the resulting colored material is fast. Illustrative of the bisphenol 35 compounds used in the present invention, are 2,2-bis-(phydroxyphenyl)propane, 2,2-bis-(p hydroxyphenyl)-heptane, 2,2-bis-(p-hydroxyphenyl)octane.

According to the most general process for preparing the heat-sensitive recording paper, the colorformers and color developers are respectively dispersed in 1 to 10 wt% water- soluble polymer solutions using a ball mill, sand mill, orthe like, then the resulting dispersions are mixed with each other and, if necessary, inorganic pigments, waxes, orthe like are added thereto, followed by coating the mixture on a base paper.

The coating amount is generally about 2 to 10 g/m 2 (as solids). The lower limit is determined by the color density upon heat coloration, whereas the upper limit is determined mainly by economical reasons.

In general heat-sensitive recording papers are prepared by dispersing respectively the foregoing the color former and color developer in 1 to 10 wt % aqueous polymer solution by means of a ball mill, sand mill, or 45 the like until an average particle size is 5 [tm or less. Representative examples of the aqueous polymer solution are polyvinyl alcohol, hydroxyethyl cellulose, starch, stylene- maleic anhydride copolymer, carboxymethyl cellulose.

Specifically, polyvinyl alcohol and hydroxyethyl cellulose are preferable. The resulting dispersions are mixed with each other at a weight ratio of the color former to the color developer (1:20 to 1:2) and then the 50 inorganic pigments such as a kaolin, aluminum hydroxide, talc, titanium oxide, zinc oxide, calcium carbonate are added, if desired.

The present invention will now be described in more detail by the following non-limiting Example. Unless indicated herein, all parts, percents, ratios, etc in the following Example are byweight.

- EXAMPLE

Preparation of Samples 1 - 4:

To 1,000 parts of pulp (L13KP.50'SR beating) dispersed in water at a concentration of 0.1 wt% were added 3 parts of a sizing solution prepared by emulsifying alkylsuccinic acid anhydride (Faibran-68 made by National Starch Co.) with cation starch (Cato-F made by National Starch Co.) in a proportion of 1:2 (by weight), and 60 made into paper of 50 g/m 2 in basis weight to obtain a support (Support A). The hot water extraction pH of this support was 7.

The thus-obtained support A was coated with one of coating solutions a, b, a', and Y having the following formulations in an amount of 6g/M2 (as solids), and dried at WC to obtain coated papers (Samples 1,2,3, and 4, respectively).

4 GB 2 031600 A 4 Coating solution a Crystal Violet lactone Bisphenol A Kaolin Polyvinyl alcohol (PVA 110 made by Kurarey Co., Ltd.) Water Coating solution b 3-Diethylamino-6-methy]-715 anilinofluoran Bisphenol A Kaolin PVA (PVA 110 made by Kurarey Co., Ltd.) Water 1 part by weight 11 11 11 63 1 part by weight 11 11 11 63 --- Coating solution a' This solution was prepared by adding 1 part by weight of a 20 % stearic acid amide emulsion (Serozole A-671 made by Chukyo Yushi Co.) to coating solution a as a sensitivity-im proving agent.

Coating solution b' This solution was prepared by adding 1 part by weight of a 20 % stearic acid amide emulsion (Serozole A-671 made by Chukyo Yushi Co.) to coating solution b as a sensitivity- improving agent.

Preparation of Comparative Samples 1 - 4: 35 To 1,000 parts of pulp dispersed at a concentration of 0.1 wt % in water were added 10 parts of reinforced 35 rosin size SIZE PINE-P made by Arakawa Rinsan Co.), then 15 parts of aluminium sulfate (calculated as Al2(S04)31 8 H20) were added thereto and made into paper of 50 g/M2 in basis weight to obtain a support (Support B). The hot water extraction pH of this support was 4.2. On the thus-obtained support B was coated, in the same manner as in Example 1, one of coating solutions 40 a, b, a', and Y used for preparing above-described Samples 1 - 4 to obtain coated papers (Samples CA, C-2, 40 C-3, and CA, respectively).

Preparation of Comparative Samples 5 and 6:

Coating solutions a'and Y (both being 6.5 in pH) were adjusted to a pH of 10.0 by adding a 1 N NaOH solution, and simultaneously coated, respectively, on support B to obtain coated papers (Samples C-5 and 45 C-6, respectively).

Preparation of Comparative Samples 7 and 8:

Coating solutions a" and b" were obtained in the same manner as with coating solutions a'and b'except using basic magnesium oxide in place of kaolin and respectively coated on support B to obtain coated 50 papers (Samples C-7 and C-8, respectively).

The above-described Samples were dried in an oven at 500C for 3 minutes and measured for initial fog density. Then, a stamp heated to 150'C was applied to the samples for 1 second with a pressure of 500 g/CM2 to determine color density. In addition, the stamp temperature was varied to determine the lower limit for forming color. This was taken as a color-forming temperature.

The color density was measured using a Macbeth reflection type densitometer, RD-504, through a visual filter.

Background fog upon storing under the conditions of high temperature and high humidity was measured in the same manner after storing the Samples for 1 week at 50'C under 80 % RH.

The results thus obtained are set forth in Table 1.

From Table 1, it is seen that the present invention provides heatsensitive recording papers forming less background fog under the conditions of high temperature and high humidity as compared with other papers.

4C v 01 zit TABLE 1

GB 2 031600 A 5 Color Heat forming Extraction Coating Temperature 5 Sample Support pH Solution (OC) 1 A 7.0 a 90 2 b 95 10 3 a' 70 4 Y 70 15 C-1 B 4.2 a 90 C-2 b 95 C-3 a' 70 20 C-4 b' 70 C-5 a' 70 (pH=10.0) 25 C-6 b' 70 (pH=10.0) C-7 all 70 30 C-8 Y 70 Background

Initial Fog 35 Color Background After

Density Fog Storing Color Remarks 1.45 0.07 0.06 blue Invention 40 1.28 0.10 0.09 black 1.26 0.08 0.08 blue 1.12 0.11 0.10 black 45 1.47 0.07 0.16 blue Comparison 1.25 0.11 0.15 black 50 1.24 0.10 0.23 blue 1.12 0.12 0.24 black 1.26 0.11 0.18 blue 11 55 1.08 0.13 0.20 black 1.22 0.10 0.17 blue 60 1.05 0.12 0.17 black 1 week at WC under 80 % RH. Background fog density higherthan 0.13 seriously deteriorates commercial values as the heat-sensitive recording paper.

6 GB 2 031 600 A

Claims

6 1. A heat-sensitive recording paper comprising abase paper having a hot water extraction pH as herein defined of from 6 to 9 and bearing on a surface thereof a heat-sensitive recording layer containing an 5 electrondonating colorless dye and an electron-accepting acidic material.
2. A paper as claimed in Claim 1, in which said acidic material is a phenolic compound.
3. A paper as claimed in Claim 2, in which said phenolic compound is a bisphenol compound represented by the followng general formula:

R 110-,n\ _Clin -OR R 2 wherein R, and R2 each represents an alkyl group containing 1 to 12 carbon atoms or R, and R2 together 15 represent a carbocyclic ring; or derivatives thereof.
4. A paper as claimed in any preceding Claim, in which said electrondonating colorless dye is selected from triaryimethane compounds, diphenyimethane compounds, xanthene compounds, thiazine compounds, and spiropyran compounds.
5. A paper as claimed in any preceding Claim, in which said base paper is a paper which has been sized 20 using a sizing agent which produces an extraction pH of from 6 to 9.
6. A paper as claimed in Claim 5, in which said sizing agent is a cationic sizing agent.
7. A paper as claimed in Claim 5, in which said sizing agent is a combination of a cationic fixing agent and an anionic sizing agent.
8. A paper as claimed in Claim 5, in which said sizing agent is an alkylketene dimer, an alky[succinic acid 25 anhydride, or a fatty acid soap containing 12 to more carbon atoms.
9. A paper as claimed in Claim land substantially as herein described.
10. A heat-sensitive recording paper substantially as herein described with reference to anyone of Samples 1 to 4 in the foregoing Examples.
11. A paper as claimed in any preceding Claim and bearing a coloured image produced by image-wise 30 exposure of the paper to heat.
12. The features as herein disclosed, or their equivalents, in any novel selection.

Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited. Croydon Surrey, 1980.

Published by the Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.

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